The present invention relates to a stationary blade shroud of a gas turbine. More particularly, this invention relates to a stationary blade shroud improved in the sealing performance in the gaps between adjacent stationary blade inside shrouds.
The turbine section of a gas turbine used in a generator or the like comprises moving blades which rotate together with the rotor, and stationary blades which are fixed in the casing. The moving blade is composed of a platform coupled to the rotor and a moving blade. The stationary blade is composed of a stationary blade and inside shroud and outside shroud fixed at both ends of this stationary blade.
The blade surface, and inside and outside shrouds of the stationary blade form a passage wall of high temperature gas flowing in the turbine section, and the blade surface and platform of the moving blade also form a passage wall of high temperature gas. In the casing, split rings for forming the passage wall of high temperature gas together with the blade surface and platform of the moving blade are fixed across a specific gap to the leading end of the moving blade. A plurality of split rings are coupled in the arraying direction of the moving blades, and a wall of an annular section is formed on the whole.
On the other hand, the moving blades and stationary blades are divided into a plurality of sections in the peripheral direction of the rotor and formed in units for the convenience of performance for absorbing thermal deformation, manufacture or maintenance, and the shrouds and platforms, like the split rings, are coupled in a plurality in the blade arraying direction, forming a wall of an annular section on the whole, and each is formed in an arc section.
When coupling the divided inside shrouds in the peripheral direction of the rotor, a gap must be held preliminarily between the coupled inside shrouds. This is because the shrouds are thermally expanded in the peripheral direction as being exposed to high temperature gas sent from the combustor of the gas turbine, and it is preferred to design so that this gap is completely eliminated in the thermally expanded state.
That is, when the high temperature gas flows in the passage formed by the blade surface, shroud, platform or split ring, the high temperature gas escapes outside through the gap formed between the coupled shrouds, and the turbine efficiency declines, or contamination may deposit in other area than the passage due to combustion gas which is high temperature gas, possibly leading to unexpected accident.
Actually, however, considering the manufacturing error and others, it is impossible to eliminate such gaps completely in high temperature condition. Accordingly, hitherto, it has been attempted to prevent escape of high temperature gas V1 from the gap 43g to outside by installing a seal member 44 between the coupled inside shrouds 43 as shown, for example, in the inside shroud 43 in FIG. 6.
More specifically, as shown in FIG. 7A that shows a section along line Ixe2x80x94I in FIG. 6 and FIG. 7B that shows a section along line IIxe2x80x94II, the seal member 44 is disposed in the groove extending in the downstream direction from the vicinity of the upstream side end 43b of flow direction of high temperature gas V1 formed in the side end 43a of the inside shroud 43.
Near the upstream side end 43b of the inside shroud 43, and along the inner circumference of the inside shroud 43, honeycomb members 43d of arc shape (shown in linear shape in FIG. 6 for the sake of simplicity) are disposed, and are provided on the inner circumference of the inside shroud 43 through a base plate 43c, and are disposed across a slight gap to seal fins 47a formed on the platform 47 of the moving blade 46 rotating as shown in FIG. 8.
The honeycomb members 43d are provided to prevent heavy contact between the rotary parts (including the platform 47) of the moving blade 46 and the stationary part including the stationary blade 42 due to rotary shaft runout of the rotating moving blades 46, and as far as the shaft runout is small, that is, in a stage of light contact before coming into heavy contact, the seal fin 47a and honeycomb member 43d contact with each other, and the honeycomb member 43d is broken. On the other hand, the seal fin 47a is higher in hardness than the honeycomb member 43d, and is not broken, and only by replacing the honeycomb member 43d, the original state is restored, and therefore the honeycomb member 43d may be called light contact detecting step for preventing heavy contact with the rotary part of the moving blade 46.
In the example shown in FIG. 6 and FIG. 7, the seal member 44 is disposed nearly along the overall length in the flow direction of high temperature gas V1 at the side end 43a of the inside shroud 43, and leak of high temperature gas V1 is nearly prevented, but in other structure of inside shroud 43, the seal member 44 cannot be disposed in the overall length of the side end 43a. 
That is, in such structure, the seal member 44 cannot be disposed because the thickness is insufficient near the upstream side end 43b of the inside shroud 43. Such structure is explained in FIG. 8 and FIG. 9.
FIG. 8 shows a stage composed of the moving blade 46 and the stationary blade 42 in the turbine section. Purge air V3 is first supplied into an outside shroud 45 to cool the outside shroud 45 as cooling air for cooling the outside shroud 45, and part of the cooling air passes through the cooling air passage formed in the stationary blade 42 to cool the stationary blade 42, and is supplied into the inside shroud 43 as cooling air, and is partly used as purge air V3.
Further, part of the purge air V3 is blown out from the gap between the moving blade 46 of the front stage and the platform 47 as shown in FIG. 8 as seal air V4, thereby preventing high temperature gas V1 from escaping from the gap between the platform 47 and inside shroud 43, but it is not desired if the blown-out seal air V4 disturbs the flow of the high temperature gas V1 too much, and it is desired to guide the seal air V4 smoothly into the flow direction of high temperature gas V1.
In order to guide the flow of the seal air V4 smoothly, as shown in FIG. 9A, the upper end corner of the inside shroud 43 is rounded, so that the seal air V4 may flow along the upper side 43b (passage side of the high temperature gas V1) of the inside shroud 43.
The cooling air passage 43e for passing the cooling air may be formed inside of the inside shroud 43. This cooling air passage 43e is formed at a deep position near the top of the inside shroud 43 so as to cool the inside shroud 43 itself and also cool the junction between the stationary blade 42 and the inside shroud 43, but when this cooling air passage 43e is formed up to the upstream side end 43b, as shown in FIG. 9A, it interferes with the cooling air passage 43e, and hence the seal member 44 cannot be disposed near the upstream side end 43b. 
As a result, as shown in FIG. 9B, near the upstream side end 43b, there is a missing range of seal member 44, and the purge air V3 may massively escape from the mixing range, and the gas turbine efficiency may be lowered.
Thus, in addition to the case of forming the upstream side end 43b of the inside shroud 43 by rounding, missing range of seal member 44 may occur due to various causes in design and structure, and anyway if missing range of seal member 44 occurs, regardless of the cause, the efficiency of the gas turbine may be lowered due to massive leak of purge air V3.
It is an object of this invention to present a stationary blade shroud capable of suppressing leak of purge air, without increasing the cost, even if a seal missing range occurs in the seal member in the gap of the inside shroud.
The stationary blade shroud according to the present invention comprises circular honeycomb members preventively broken by contact with rotary parts of moving blades disposed along the inner circumference of inside shroud of each stationary blade divided into plural parts in the peripheral direction. The honeycomb members are disposed as being deviated in the peripheral direction with respect to the stationary blade inside shroud so as to plug the gaps formed between adjacent stationary blade inside shrouds.
Herein, by xe2x80x9cpreventively broken by contact with rotary parts of moving bladesxe2x80x9d it means that they are broken by a light contact in a stage before causing heavy contact with the rotary parts of the moving blades, so that major damage by heavy contact can be prevented.
The honeycomb members may be disposed so that the honeycomb extending direction may or may not coincide with the purge air flow direction (direction from inner circumference side of inside shroud to outer circumference side, that is, turbine radial direction), but when disposed so that the honeycomb extending direction coincides with the purge air flow direction, the purge air passes through the honeycomb, and it is preferred to install a base plate to plug the opening of the honeycomb. However, since the honeycomb members hitherto used for the purpose of preventing heavy contact are disposed in the inside shroud through such base plate from the beginning, and it is enough to use honeycomb members having such base plate.
According to the stationary blade shroud, since the existing honeycomb members provided to prevent heavy contact also play the role of plugging the gaps formed between the inside shrouds of the stationary blades, leak of purge air can be suppressed. New constituent elements are not additionally needed to plug the gaps, and the increase of cost is prevented.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.